This invention relates generally to recirculating document feeders, and more particularly to a recirculating document feeder capable of presenting sheets of simplex or duplex documents to a copier apparatus in a manner which enables the copier apparatus to reproduce collated sets of such documents at a reproduction rate which makes maximum use of the full reproduction rate of the copier apparatus.
Today's commercially available copier apparatus are capable of making reproductions at a significant rate (e.g., seventy to one hundred copies per minute). Such high reproduction rates are possible, at least in part, due to advances in document feeders for automatically presenting documennt sheets to the copier platen, and in the copier apparatus itself. For example, U.S. Pat No. 4,176,945 (issued Dec. 4, 1979, in the name of Holzhauser et al) shows a high speed copier apparatus and a recirculating document feeder associated with such copier apparatus. Such arrangement is capable of producing simplex (one sided) or duplex (two sided) copy on a receiver sheet on a single pass of such sheet through such apparatus in order to accomplish a high reproduction rate.
The structure of the aforementioned U.S. Pat. No. 4,176,945 in a simplex mode of operation, circulates document sheets seriatem from a hopper to the copier platen and back to the hopper at a rate which enables reproductions to be made in collated order at a rate which fully utilizes the high reproduction rate of the copier. In a duplex mode of operation, the structure circulates document sheets seriatem from the hopper, across the copier platen to a turn-over mechanism, back to the platen where one side is exposed, again to the turn-over mechanism and back to the platen where the opposite side is exposed, and then back to the hopper. Such sequence, which is necessary to assure reproduction of the document sheets in a proper order to obtain collated output, does not fully utilize the high reproduction rate of the copier apparatus due to the extended length of the path traveled by the document sheets to the turn-over mechanism before exposure of each side of the sheets.